JPS60257408A - Optical fiber and its production - Google Patents

Abstract

PURPOSE:To suppress the capture of hydrogen atoms to a defective part and to improve eventually the long-period stability and reliability of an optical fiber by incorporating fluorine into the core part and clad part respectively of the fiber and generating a difference in refractive index from the relative difference in the concentrations of fluorine in both parts. CONSTITUTION:The fine glass particles formed by supplying SiCl4 into, for example, an oxyhydrogen flame and decomposing the same are deposited and grown axially to manufacture a porous glass body having a circular columnar shape. Such porous glass body is subjected to a heating treatment at 1,200 deg.C in a gaseous helium atmosphere contg. thionyl fluoride SOF2 and is then heated up to 1,500 deg.C in gaseous helium by which said body is made transparent and glassy. The pulverous glass particles formed as a result of the decomposition of the SiCl4 by the oxyhydrogen flame is deposited on the outside circumference of the quartz glass rod to form a glass layer for cladding. Such glass rod is subjected to a heating treatment to 1,500 deg.C in a gaseous helium atmosphere contg. Si2OF6 by which the glass layer is melted and made transparent. The clad glass is thus formed. The refractive index of such clad glass layer is lower than the refractive index of the glass rod.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical fiber and a method for manufacturing the same, and in particular, the core part and cladding part constituting the optical fiber are each made of silica glass containing fluorine, and the relative proportion of fluorine is An object of the present invention is to provide an optical fiber having a structure in which a difference in refractive index is caused by a difference in concentration.

Conventionally, a step-index optical fiber is known as an optical fiber, which is composed of a core having a high refractive index and a cladding having a lower refractive index than the core around the core. Quartz glass doped with a metal oxide to increase the refractive index is used as the core part, and ordinary high-purity quartz glass is used as the cladding part. The doping agent (metal oxide) should have no absorption in the wavelength range, be easily dissolved in quartz glass, and be easy to handle as the raw material compound is liquid at room temperature.
OeO□ is used because it is easy to purify. However, G e O2 is scarce in terms of resources, is expensive, and has poor radiation resistance, resulting in increased loss over time.

In order to solve this drawback, an optical fiber with a structure in which high-purity quartz glass is used in the core part and dopants that lower the refractive index such as fluorine and boron are added to the cladding part has been proposed. There is a problem in that structural defects such as oxygen defects occur in high-temperature melting yarns, and hydrogen molecules are captured in these defects, resulting in increased light absorption loss.

111 The present inventors conducted extensive research to solve these disadvantages, and found that in an optical fiber consisting of a core and a cladding made of silica glass, the core and cladding are The inventors have discovered that extremely excellent results can be obtained by incorporating fluorine into each, and creating a structure in which a difference in refractive index is caused by the relative concentration difference between the two fluorine-containing groups, and the present invention has been completed. .

(Summary of the present invention) 1. A quartz glass core containing fluorine with a low lfi and a quartz glass cladding containing high concentration of fluorine and having a refractive index lower than that of the core formed around this core. Optical fiber consisting of parts.

2. A porous glass body obtained by depositing and growing glass particles produced by flame hydrolysis of a glass raw material compound in a cylindrical shape is heated in an atmosphere containing a fluorine compound L7, and is melted and made transparent to obtain a low concentration of fluorine. Next, glass fine particles produced by flame hydrolysis of frit compounds are deposited and grown around this core glass rond, and this F7i layer is heat-treated in an atmosphere containing fluorine compounds. A method for producing an optical fiber, which comprises obtaining a glass preform for an optical fiber by melting and making it transparent to form a cladding glass layer containing a high concentration of fluorine, and melt-spinning the preform.

According to the present invention, since fluorine is strongly bonded to the oxygen defect portion, the capture of hydrogen molecules to the defect portion is suppressed, and as a result, the long-term stability reliability of the optical fiber is improved. This gives you the advantage of

The present invention will be explained in detail below.

The optical fiber of the present invention has the above-mentioned structure, but in order to manufacture it, first a glass iron for the core made of quartz glass containing a low concentration of fluorine is formed around the core glass iron, and a Kf!
It is necessary to create a glass matrix consisting of a silica glass cladding glass layer containing a certain amount of fluorine. That is, a glass raw material gas containing a hydrolyzable or oxidatively decomposable silicon compound such as silicon tetrachloride is supplied into a flame such as an oxyhydrogen flame (°C) and subjected to a decomposition reaction to produce glass fine particles. This is deposited and grown sequentially in the axial direction to create a cylindrical porous glass body.Next, this porous glass body is heated with an inert gas such as helium gas containing a low concentration of fluorine compounds (content of 1 mol% or less). Approximately 1 in the atmosphere
The glass rod is heat-treated at a temperature of 000 to 1600'C to melt and become transparent, thereby producing a transparent glass rod containing fluorine in a predetermined agglomerate.

The heating operation for melting and transparency may be performed either in an atmosphere containing the fluorine or in an atmosphere containing only an inert gas.

The fluorine content in this glass rond is desirably a low concentration content that is 0.01 to 0.1% lower than the refractive index of high-purity quartz glass. This makes it difficult to provide a refractive index difference with the cladding layer, and on the other hand, if it is too small, it is impossible to prevent the harmful effects of oxygen defects g2. Such low-concentration fluorine-containing glass ronds are made mainly from glass raw materials and silicon compounds such as silicon tetrachloride.

It can also be produced by adding a small amount of a glass raw material compound containing fluorine atoms to this mixture, subjecting it to flame hydrolysis to produce and deposit fluorine-containing glass particles, and then heating and melting the particles.

Next, glass fine particles produced by flame hydrolysis of a glass raw material compound whose main component is a silicon compound such as silicon tetrachloride are deposited and grown around the quartz glass rod, and an inert gas such as helium gas containing a fluorine compound is used. This deposited layer is heat-treated in an atmosphere to a temperature of approximately 1000 to 1600°C to melt and become transparent, resulting in a predetermined density of 15%.
A transparent glass layer for cladding containing fluorine is formed. Glass 1 The accumulation of glass particles around the glass 13° 19. ．． . A. Care 1. This is done by moving the burner flame relatively back and forth so that it is deposited uniformly in the radial direction of the glass rod. The concentration of the fluorine compound in the inert gas atmosphere during heat treatment of this deposited layer is preferably a relatively high value of 1 to 10 mol % for the purpose of obtaining a cladding layer with high fluorine content. The heating operation for melting and transparency may be performed either in an atmosphere containing the fluorine or in an atmosphere containing only an inert gas. The fluorine content in the cladding layer thus obtained is required to be at least 0.2% lower than the refractive index of high-purity quartz glass. Note that, if necessary, the outermost part may be covered with quartz glass by a rod-in-tube method or an external OVD method.

The frit compound used in the present invention is a flame-hydrolyzable silicon compound, with the general formula RmSix,
-TTlC In the formula, R is a monovalent hydrocarbon group such as a methyl group or an ethyl group or a hydrogen atom, integer), for example 5
ICL, , SiF4, H81C! tSiH% CH3
5iCL3.3% 4 CH3Si (OCH3)3, si (QC!H3
)4, Si(OC2Hs)4, and the like. Generally, 5icz4 is used.

Fluorine compounds for fluorine conductors in glass rods and cladding include fluorocarbon, fluorochloride, sulfur fluoride, silicon fluoride.

Boron fluoride, phosphorus fluoride, oxyfluoride, sulfur, silicon oxyfluoride, etc. are used, specifically CF4,
O, F6, CCl2F3, CF2Cl.

ccty3, SF3, SF%5iF4. Si
, F',, BF PF % POF SOF , S O
, F2.3II$3' 2 Si OF % 8i302F, and the like. Among these, sulfur oxyfluoride and silicon oxyfluoride, which have both fluorine and oxygen in their molecules, are excellent as fluorine doping agents.

The glass base material for optical fiber, which is manufactured by the method described above and is made of a lath rod containing a low concentration of fluorine and a cladding containing a high concentration of fluorine, can be made into a glass fiber by heating and melting and spinning using a conventionally known method. be done.

Since the optical fiber according to the present invention contains fluorine in the core and cladding parts, structural defects such as oxygen defects occur in the silica glass, and the tendency for optical loss to increase is extremely small, especially in a hydrogen atmosphere. (It has excellent long-term stability).It also has excellent radiation resistance and is extremely reliable. Moreover, since expensive G e O2 is not used as a dopant, it is advantageous in terms of cost.

Next, specific examples will be given.

Example Using a quartz quadruple tube burner, )T, 67/min and 0□10
! 380y of 5xat4 in an oxyhydrogen flame formed at
Glass fine particles produced by supplying and decomposing at a rate of d1 were deposited and grown in the axial direction to form a cylindrical porous glass body.

This porous glass body was treated with 0.5 mol% thionyl fluoride SO
2 at a temperature of 1200°C in a helium gas atmosphere containing F.
The material was heat treated for a period of time, and then heated to 1500° C. in helium gas to form transparent glass.

The refractive index of the silica glass rod thus obtained was 0.05% lower than the refractive index of silica glass.

In Fig. 1, 1 = 0.05%0.Next, 5ic was applied to the outer periphery of this quartz glass rod using the same oxyhydrogen flame as above.
Glass particles produced from the decomposition of t4 were deposited to form a cladding glass layer (porous glass layer). This material was heated to 1,500° C. in a helium gas atmosphere containing 4 mol % of 5i20F6, and was melted and made transparent to form a clad glass. The refractive index of this cladding glass layer is 0.3 with respect to the refractive index ζ2 of the glass rod.
The value was 3% lower. In Figure 1, △2-(133
%, l The glass base material for optical fiber obtained by the above 4+2
When the fiber was spun at a speed of 3 m/s in a high-temperature furnace at 00°C, a single mode optical fiber with a core diameter of 9 μm and an outer diameter of 12,511 m was obtained.

This optical fiber has a refractive index distribution as shown in Fig. 1, where refractive index nl of nO disilica glass: refractive index n2 of core: refractive index Δl of cladding: difference in refractive index of core with respect to quartz glass ( %) to 2:
Difference in refractive index between core 1 and cladding -'%) Also 1, 3
The transmission loss in μ'm was 0.42 dB/km, which was extremely excellent.

Furthermore (1.39 after heating 500 m of this optical fiber in the presence of hydrogen gas for 72 hours at 200°C and before heating)
The transmission loss in μm was as shown in Table 1.

For comparison, the same table also shows the results of similar tests performed on optical fibers manufactured using a fluorine-free quartz glass rod core material obtained by the conventional method.

Table 1 Transmission loss (1.39 μm) Example 2 A quartz glass tube was placed over the optical fiber glass base material produced in Example 1, and this material was melt-spun in the same manner as in the previous example, resulting in the following results as shown in Figure 2. An optical fiber with a refractive index distribution was obtained. Each symbol in the figure has the same meaning as in FIG. 1.

[Brief explanation of drawings]

FIG. 1 shows the refractive index distribution of the optical fiber manufactured in Example 1, and FIG. 2 shows the refractive index distribution of the optical fiber manufactured in Example 2. Patent applicant Shin-Etsu Chemical Co., Ltd.

Claims (1)

[Scope of Claims] 1. A quartz glass core containing a low concentration of fluorine and a quartz glass cladding containing a high concentration of fluorine and having a refractive index lower than that of the core formed around the core. optical fiber. 2. A porous glass body obtained by depositing and growing glass particles produced by flame hydrolysis of glass raw material compounds in a cylindrical shape is heat-treated in an atmosphere containing a fluorine compound to melt and make it transparent, thereby removing a low concentration of fluorine. Next, glass fine particles produced by flame hydrolysis of frit compounds are deposited and grown around the core glass rond, and this deposited layer is heated in an atmosphere containing fluorine compounds. A method for producing an optical fiber, which comprises obtaining a glass material for an optical fiber in which a cladding layer containing a high concentration of fluorine is formed by melting and making it transparent, and melt-spinning the material.